It's a giant mess. I don't think Pot would have gained the support/power that he did without the US indiscriminate bombing. Much like the creation of ISIS and the strengthening of the Taliban in Afghanistan, it turns out people don't like the people dropping bombs on them. They'll turn to whoever is fighting the bombers.
The US involvement in Vietnam would have already been over before the uprising of Pot had Nixon and Kissinger not skuttled peace talks to help Nixon get elected.
It’s not like Cambodia was a stable democracy before the bombings.
The Khmer Rouge and other opposition groups were fighting the government in an armed conflict since 1950. The Khmer Rouge controlled almost half of Cambodia’s territory 10 years before the bombing.
In the grand scheme of Cambodias civil war, the US bombing didn’t play that big a role at all.
You can point the fingers everywhere, you can also say the French were at fault because of the core of the Khmer Rouge group were scholarship students who were sent to France to study socialism, came back with that education and used to to establish the Khmer Rouge.
It's not exactly true, Pol Pot went to France on a scholarship to become an electrical engineer. When he came back to Cambodia, he worked as a literature teacher.
The ideological content of the Khmer Rouge is very poor overall, and is a mix between nationalism and communism aiming to "clean" the nation from western influences. Which is kind of ironic given Pol Pot's background.
The US involvement in Vietnam would have already been over before the uprising of Pot had Nixon and Kissinger not skuttled peace talks to help Nixon get elected.